Method and apparatus for managing mobility in wireless communication system

ABSTRACT

The present disclosure in an aspect provides a method of managing mobility of a UE in a wireless communication system, including 1) determining in an RRC inactive state (an RRC inactive mode), whether to change a serving cell that is currently attached, 2) when determining to change the serving cell, receiving a system information from a target cell, and checking, based on the system information, whether a base station that controls the serving cell is identical to or different from a base station that controls the target cell, and 3) depending on identity or difference between the base station that controls the target cell and the base station that controls the serving cell, performing i) releasing an RRC-connection to thereby transition into an idle state, or ii) a cell change procedure to the target cell.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a Continuation Application of U.S. application Ser.No. 16/468,212, filed Jun. 10, 2019, which is a U.S. National StageApplication under 35 U.S.C. § 371 of PCT Application No.PCT/KR2017/015465, filed Dec. 26, 2017, which claims priority to KoreanPatent Application No. 10-2017-0097743, filed Aug. 1, 2017, whose entiredisclosures are hereby incorporated by reference.

FIELD OF INVENTION

The present disclosure in some embodiments relates to a method andapparatus for mobility management in a wireless communication system.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and do not necessarily constituteprior art.

A terminal attached to a network in an existing wireless communicationsystem (e.g., EPS or LTE) has two states of “ECM-CONNECTED” and“ECM-IDLE” selectively based on the presence or absence of a non-accessstratum (NAS) signaling connection (or ECM connection). For the ECMconnection, the terminal and a base station need to have a radioresource control (RRC) connection established therebetween, anddepending on its RRC connection or non-RRC connection, the terminal hastwo states of “RRC-CONNECTED” and “RRC-IDLE” selectively. In theRRC-CONNECTED state, which is also referred to as a connected mode, theterminal can immediately transmit/receive data when generated. However,this requires the terminal to have handover and measurement proceduresfor mobility support. Meanwhile, in the RRC-IDLE state which is alsocalled an idle mode, the terminal can not immediately transmit/receivedata when generated, but it requires no handover and measurementprocedures. However, for the idle state to transmit and receive datawhen generated, it needs to transition to a connected mode, involvinggeneration of signaling and a transfer delay or latency in the process.

SUMMARY

The present disclosure in some embodiments seeks to provide a method andapparatus for mobility management in a wireless communication system,which can relieve a UE of signaling load and battery consumption andreduce the system latency by introducing a new state capable of reducinga load on the UE in its connected mode while taking advantage of thestrength in the connected mode of the UE.

At least one aspect of the present disclosure provides a mobilitymanagement method of a user equipment (UE) in a wireless communicationsystem, including 1) determining, in an RRC inactive state (an RRCinactive mode), whether to change a serving cell that is currentlyattached, 2) when determining to change the serving cell, receiving asystem information from a target cell, and checking, based on the systeminformation, whether a base station that controls the serving cell isidentical to or different from a base station that controls the targetcell, and 3) depending on identity or difference between the basestation that controls the target cell and the base station that controlsthe serving cell, performing i) releasing an RRC-connection to therebytransition into an idle state, or ii) a cell change procedure to thetarget cell.

At least one aspect of the present disclosure provides a mobilitymanagement method of a base station in a wireless communication system,including 1) receiving a cell change request message from a userequipment (UE) in an RRC inactive state (an RRC inactive mode), 2)checking whether the base station is identical to or different from abase station that controls a target cell to which a cell change wasrequested by the UE, and 3) depending on identity or difference betweenthe base station and the base station that controls the target cell,performing i) a handover procedure to the base station that controls thetarget cell, or ii) a cell change procedure to the target cell.

At least one aspect of the present disclosure provides a terminal devicefor managing mobility in a wireless communication system, including atransceiver unit configured to transmit and receive signals, and acontrol unit. The control unit is configured to determine, in an RRCinactive state (an RRC inactive mode), whether to change a serving cellcurrently attached. The control unit is further configured to, upondetermining to change the serving cell, receive a system informationfrom a target cell, checking, based on the system information, whether abase station that controls the serving cell is identical to or differentfrom a base station that controls the target cell, and depending onidentity or difference between the base station that controls theserving cell and the base station that controls the target cell, performi) releasing an RRC connection to thereby transition into an idle state,or ii) a cell change procedure to the target cell.

At least one aspect of the present disclosure provides a base stationapparatus for managing mobility in a wireless communication system,including a transceiver unit configured to transmit and receive signals,and a control unit. The control unit is configured to receive a cellchange request message from a user equipment (UE) in an RRC inactivestate (an RRC inactive mode), and check whether the base stationapparatus is identical to or different from a base station that controlsa target cell to which a cell change was requested by the UE. Thecontrol unit is further configured to, depending on identity ordifference between the base station apparatus and the base station thatcontrols the target cell, perform, i) a handover procedure from the basestation that controls the target cell, or ii) a cell change procedure tothe target cell.

According to some embodiments of the present disclosure, compared to theRRC-connected state of a user equipment (UE), the battery consumption ofthe UE and the network signaling load thereon can be greatly reduced. Inaddition, the data latency can be significantly reduced compared to theRRC-idle state.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a state model of a user equipment (UE) in a wirelesscommunication system according to at least one embodiment of the presentdisclosure.

FIG. 2 is a flowchart of a mobility management method of a base station,according to at least one embodiment of the present disclosure.

FIG. 3 is a flowchart of a mobility management method of a UE, accordingto at least one embodiment of the present disclosure.

FIG. 4 is a flowchart of a paging procedure performed after a UE in RRCinactive state releases an RRC-connected state due to a cell change,according to at least one embodiment of the present disclosure.

FIG. 5 is a flowchart of a paging procedure performed after a UE in RRCinactive state releases an RRC-connected state due to a cell change,according to another embodiment of the present disclosure.

FIG. 6 is an exemplary diagram of a plurality of cells controlled by asingle base station and moving UEs in an RRC inactive state.

FIG. 7 is a flowchart of a mobility management method of a base station,according to yet another embodiment of the present disclosure.

FIG. 8 is a flowchart of a mobility management method of a UE, accordingto yet another embodiment of the present disclosure.

FIG. 9 is a flowchart of a mobility management method of a UE, accordingto yet another embodiment of the present disclosure.

FIG. 10 is a schematic diagram of a configuration of a base stationapparatus according to at least one embodiment of the presentdisclosure.

FIG. 11 is a schematic diagram of a configuration of a terminal deviceaccording to at least one embodiment of the present disclosure.

DETAILED DESCRIPTION

Before specific description of the present disclosure, examples ofinterpretable meanings of the terms used herein are provided. However,it should be noted that the following examples are not meant to belimiting.

A base station is an entity communicating with a UE, and provide a linkto a core network. The base station may be referred to as a BS, a NodeB(NB), an eNodeB (eNB), a gNodeB (gNB), or the like.

A user equipment is an entity communicating with a base station, and maybe fixed or mobile. A user equipment may be referred to as a UE, amobile station (MS), a mobile equipment (ME), a terminal, or the like.

Access and Mobility Management Function (AMF) is the termination of aRadio Access Network (RAN) Control Plane (CP) interface (e.g., N2), andterminates Non-Access Stratum (NAS). The AMF supports functions such asregistration management, connection management, reachability management,mobility management, access authentication and access authorization. TheAMF may be implemented in a form that software of the above functions isloaded on a single virtualized network device. In other words, the AMFmay be implemented as a virtualized node rather than a physical node.

User Plane Function (UPF) supports functions such as anchor points forIntra/Inter-RAT mobility, external PDU session points forinterconnection to the data network, packet routing and forwarding, userplane portions of packet inspection and policy rule enforcement, trafficusage reporting, uplink classification supporting traffic flow routingto the data network, uplink traffic verification, downlink packetbuffering, downlink data notification triggering, or the like. The UPFmay be implemented in a form in which software of the above functions isloaded on a single virtualized network device. In other words, the UPFmay be implemented as a virtual node rather than a physical node.

This specification illustrates a wireless communication system capableof providing a multiple connectivity service to a UE by linking aplurality of different wireless access technologies where an existingwireless communication system coexists with a next generation wirelesscommunication system. At least one embodiment of the present disclosurewill be described taking a Long Term Evolution (LTE) or 4G system as anexample of a conventional wireless communication system, and taking a 5Gsystem or a New Radio (NR) system as a next generation wirelesscommunication system. However, this is only an example, and otherwireless communication system may be included at least partly.

Hereinafter, some embodiments of the present disclosure will bedescribed in detail with reference to the accompanying drawings. In thefollowing description, like reference numerals designate like elements,although the elements are shown in different drawings. Further, in thefollowing description of some embodiments, a detailed description ofknown functions and configurations incorporated therein will be omittedfor the purpose of clarity and for brevity. In addition, the terms suchas “unit,” “module,” and the like refer to units for processing at leastone function or operation, which may be implemented by hardware,software, or a combination thereof.

FIG. 1 is a state model of a UE in a wireless communication systemaccording to an embodiment of the present disclosure.

In the wireless communication system according to at least oneembodiment of the present disclosure, there are two types ofregistration management (RM) states, “RM-DEREGISTERED” and“RM-REGISTERED,” depending on whether or not the UE is registered withthe network in the selected PLMN. In the RM-REGISTERED state, the UE hastwo connection management (CM) states, “CM-IDLE” and “CM-CONNECTED,”depending on whether or not a Non-Access Stratum (NAS) signalingconnection is established with Access and Mobility Management Function(AMF). Here, the NAS signaling connection includes both an accessnetwork (AN) signaling connection between the UE and the base stationand an N2 connection between the base station and the AMF. An example ofan AN signaling connection is a Radio Resource Control (RRC) connection.

The UE in the CM-IDLE state, while it establishes no NAS signalingconnection with the AMF, may perform cell selection, cell reselection,and PLMN selection. The UE in the CM-CONNECTED state, while itestablishes the NAS signaling connection with the AMF, may have thestatus details of “RRC-ACTIVE” and “RRC-INACTIVE.” When the UE is in theRRC-INACTIVE state (hereinafter can be also referred to as ‘RRC inactivemode’), the following applies.

UE, reachability managed by the base station by using the supportinformation from the core network

UE, paging managed by the base station

UE, monitoring the paging by using the core network and base stationidentification information

In the RRC inactive state, the NAS signaling connection is maintainedbetween the UE and the AMF, but the RRC-connected state is inactivatedbetween the UE and the base station. This RRC inactive state reduces thesignaling load and latency due to the transition between the existingRRC-CONNECTED state (hereinafter referred to as ‘connected state’) andthe RRC-IDLE state (hereinafter referred to as ‘idle state’), andreduces UE battery consumption. The introduction of this RRC inactivestate can support an appropriate level of service quality and mobilityin consideration of a service characteristic of a user. In the RRCinactive state, the cell to which the UE connects or camps may bechanged by the movement of the UE or the change of the radio state.

As a technology for supporting an RRC inactive state, the presentdisclosure in some embodiments provide a mobility management method andapparatus capable of effectively updating a cell change when the cell ischanged due to movement of a UE in the RRC inactive state or due to aradio state change. Hereinafter, some embodiments will be described indetail with reference to the drawings.

FIG. 2 is a flowchart of a mobility management method of a base station,according to an embodiment of the present disclosure.

The base station transmits a measurement configuration to a UE in StepS210. The measurement configuration is a configuration related towhether to report the received signal strength to the base station whenan event occurs to the UE. The measurement configuration may betransmitted to the UE through an RRC connection reconfiguration messagewhen the base station establishes the RRC-connected state with the UE,or it may be transmitted to the UE after the UE transitions from itsconnected state to the RRC inactive state. Upon receiving themeasurement configuration, the UE measures the received signal strengthof the serving cell and the neighboring cells until it detects therelevant event (i.e., triggering event for causing reporting of ameasurement result) for sending a measurement report message for themeasurement result.

The UE may transmit the measurement report to the base station followinga predetermined condition even after the transition to the RRC inactivestate. When the base station receives the measurement report accordingto the measurement configuration from the UE in RRC inactive state(S220), the base station determines, based on various informationincluding the received measurement report, whether to change the servingcell currently being accessed by the UE in RRC inactive state (S230).The base station may determine whether a change of the serving cell isneeded and, if yes, to which cell the serving cell is to be changed.

The base station determines, upon determining to change the servingcell, whether it is the same base station as the controlling station ofthe target cell, that is, whether the serving-cell controlling BS isidentical to or different from the target-cell controlling BS (S240). Inother words, the base station determines whether the target cell belongsto the cells it controls. The base station performs, base on thedetermination result, a handover procedure to a base station thatcontrols the target cell, or a cell change procedure to the target cell.Specifically, when the base station determines that it is not atarget-cell controlling BS, it performs the handover procedure to thetarget-cell controlling BS (S250). Otherwise, when the base stationdetermines that it is the target-cell controlling BS, it performs thecell change procedure to the target cell (S260).

The base station, in the cell changing procedure, may update the cellinformation in the previously stored context information of the UE inRRC inactive state, and transmit the updated cell information to the UEin RRC inactive state. The updated cell information may include at leastone of an identifier of the target cell, a temporary identifier of theUE, resource allocation information, information for ciphering, andinformation for an integrity check.

FIG. 3 is a flowchart of a mobility management method of a UE, accordingto at least one embodiment of the present disclosure. The UE of thisembodiment is in the RRC inactive state.

The UE in RRC inactive state determines whether to change the currentlyconnected serving cell (S310). At this time, the UE may determinewhether to change the serving cell based on at least one of a radiosignal strength of a serving cell, a radio signal strength of one ormore neighboring cells, an offset of the serving cell and each of one ormore neighboring cells, and how long a condition for the UE to make acell change lasts. Determining whether or not to change the serving cellmay also include determining the target cell to be changed. In thisembodiment, the UE in RRC inactive state does not provide themeasurement report to the base station, and therefore, the UE determinesthe cell change autonomously.

When it determines to change the serving cell, the UE in RRC inactivestate receives system information from the target cell (S320). Here, thesystem information includes essential information and optionalinformation as information that one cell broadcasts. For example,essential system information may include Master Information Block (MIB),System Information Block (SIB) 1, and SIB 2. The UE may obtain, from thesystem information, the cell identifier and information on the basestation that controls the cell.

The UE in RRC inactive state determines, based on the received systeminformation, whether the base station controlling the target cell isidentical to or different from the base station controlling the servingcell (S330). The UE may determine the identity or difference based onthe target cell identifier obtained from the system information, andinformation on the base station controlling the target cell.

The UE in RRC inactive state performs, depending on the identity ordifference between the base station controlling the target cell and thebase station controlling the serving cell, i) releasing the RRCconnection with the base station to which the UE currently registered,to thereby transition to the idle state, or ii) the cell changeprocedure to the target cell. Specifically, when the base stationcontrolling the target cell is not identical to the base stationcontrolling the serving cell, the UE transitions from the RRC inactivestate to the idle state (S340), and if not, it performs the cell changeprocedure to the target cell (S350). The cell change procedure to thetarget cell in the currently connected base station may be started bythe UE transmitting the cell change request message includinginformation on the target cell to the base station.

When Step S340 causes the RRC-connected state to be released and the UEenters the target cell controlled by the new base station, the UE isunable to receive the paging transmitted by the existing base station atthe occurrence of mobile terminated (MT) data (i.e., downlink data).Therefore, there is a need for techniques that can effectively handlepaging in such situations. Hereinafter, some embodiments as for thetechniques will be described in detail with reference to FIGS. 4 and 5.

FIG. 4 is a flowchart of a paging procedure performed after a UE in RRCinactive state releases RRC-connected state due to a cell change,according to an embodiment of the present disclosure. In FIG. 4, an oldbase station (old BS) refers to a base station to which the UE in RRCinactive state had been attached before it transitioned to the idlestate according to the cell change, that is, the base station thatcontrols the serving cell. A new base station (new BS) refers to a basestation after change following a cell change performed by the UE in RRCinactive state, that is, the base station that controls the target cell.

In the present embodiment, the UE in RRC inactive state transitions tothe idle state as shown in FIG. 3, following a change of cell to thecell controlled by the new base station that is not currently attached(S410). When downlink data is generated for the UE, the User PlaneFunction (UPF) transmits the downlink data (GTP-U packet) to the old BS(S412).

The old BS transmits to the UE, a message informing the downlink datageneration (data notification message) or a paging message (S414). Atthis time, the old BS may use a temporary identifier (e.g., L2 ID) ithas assigned to the UE. However, the UE cannot receive a message fromthe old BS since the UE is in idle state after the RRC-connected statewith the old BS was released. Accordingly, the UE fails to receive thedata notification message or the paging message (S416).

The old BS does not have a paging response from the UE, so it canrecognize that the current UE cannot receive paging (S418). In otherwords, the old BS can detect the mobility of the UE. Accordingly, theold BS may transmit a message including at least one of a paging requestand a notification that the UE is in unreachable status to the AMF(S420). At this time, the old BS may transmit the relevant message afterincluding downlink data received from the UPF to the AMF.

The AMF is responsive to the message received from the old BS fortransmitting a paging request message to the new BS (S422). At thistime, the AMF may use a temporary identifier (e.g., L3 ID) that it hasassigned to the UE. In Step S422, the AMF may send a paging requestmessage to one or more base stations including the new BS. For example,when a tracking area (TA) is set for each base station (that is, when agroup of cells controlled by one base station is set as TA), the AMF issupposed to transmit a paging request message only to the new BS. Asanother example, when a TA is set up for each group of a plurality ofbase stations, the AMF transmits a paging request message to a pluralityof base stations including a new BS belonging to one TA.

The new BS in receipt of the paging request message from the AMFperforms a paging process with the UE (S424). The UE is responsive tothe paging message from the new BS for performing a service requestprocedure (S426). In accordance with the service request procedure, theUE establishes an RRC-connected state with a new BS. Accordingly, thenew BS receives the downlink data transferred from the AMF (S428), andtransmits it to the UE (S430).

FIG. 5 is a flowchart of a paging procedure performed after a UE in RRCinactive state releases an RRC-connected state due to a cell change,according to another embodiment of the present disclosure.

In this embodiment, Steps S510 to S526 are similar to Steps S410 to S426of FIG. 4 described above, so a detailed description thereof will beomitted. However, different from that of FIG. 4, when the old BS in thisembodiment transmits a message including at least one of a pagingrequest and a notification that the UE is in unreachable status to theAMF (S520), it does not transmit downlink data received from the UPF.

When the UE is responsive to the paging for performing a service requestprocedure, whereby establishing an RRC-connected state with a new BS(S526), the old BS transmits its received downlink data for the UE backto the UPF (S528). The reason for this may be that the downlink dataretransmission is required due to the base station change. In otherwords, the old BS may transmit the downlink data back to the UPF, and itmay request that the retransmission be forwarded to the new BS.

The UPF transmits the downlink data received from the old BS to the newBS in Step S530, and receives the downlink data through the new BS inStep S532.

FIG. 6 is an exemplary diagram of a plurality of cells controlled by asingle base station and moving UEs in an RRC inactive state.

A plurality of cells controlled by one base station may be divided intoborder cells and inner cells. A border cell is a cell close to a borderbetween base stations, and means a cell adjacent or close to a cellcontrolled by another base station. A border cell is a cell located in acertain range from a border between base stations, and may be variouslyset according to an embodiment. The inner cell means a cell belonging toan area surrounded by border cells. In FIG. 6, the border cells arerepresented by hatched areas, the UEs 610 and 630 in RRC inactive stateare located in the inner cells, and the UE 620 in RRC inactive islocated in the border cell.

In general, when a UE is located in a border cell, it is close to a cellcontrolled by another base station. Therefore, cell change is highlylikely to change the base station. In other words, a UE located in aborder cell is likely to make a cell change to a cell controlled byanother base station. Accordingly, in the mobility management in the RRCinactive state, distinguishing the case where the UE is located in theborder cell from the case where the UE is located in the internal cell,can more efficiently reduce battery consumption and signaling load ofthe UE. Hereinafter, this will be described in detail with reference toFIGS. 7 to 9.

FIG. 7 is a flowchart illustrating a mobility management method of abase station, according to yet another embodiment of the presentdisclosure.

In at least one embodiment, the UE in RRC inactive state autonomouslydetermines the cell change without providing a measurement report to thebase station, and the base station receives the cell change requestmessage from the UE when the cell is changed by the UE in RRC inactivestate. However, when the UE in RRC inactive state is located in theborder cell (i.e., when the base station is likely to change), the basestation provides the measurement report to the base station. The UE inRRC inactive state located in the border cell can prevent the occurrenceof paging loss as shown in FIGS. 4 and 5 by providing the measurementreport to the base station.

Referring to FIG. 7, the base station receives a cell change requestmessage from a UE in RRC inactive state (S710). The base station inreceipt of the cell change request message, checks whether it isidentical to the base station that controls the target cell to which theUE has requested the cell change (S720). The base station performs,depending on the identity or difference between the base station inreceipt of the message and the base station controlling the target cell,a handover procedure to a base station that controls the target cell, ora cell change procedure to the target cell.

When the base station in receipt of the message finds it is notidentical to the base station controlling the target cell, it performsthe handover procedure to the base station that controls the target cell(S730). When it find it is the same, the base station performs the cellchange procedure to the target cell (S740). The base station, in thecell changing procedure, may update the cell information in thepreviously stored context information of the UE in RRC inactive state,and transmit the updated cell information to the UE in RRC inactivestate. The updated cell information may include at least one of anidentifier of the target cell, a temporary identifier of the UE,resource allocation information, information for ciphering, andinformation for an integrity check.

After the start of the cell changing procedure, the base station maycheck whether the target cell is a border cell (S750). When itdetermines that the target cell is a border cell, the base station mayinstruct to transmit the measurement report to the UE in RRC inactivestate (S760). For the purpose of instructing to transmit the measurementreport, the base station may send the measurement configuration to theUE in RRC inactive state. Upon receiving the measurement configuration,the UE in RRC inactive mode transmits the measurement report to the basestation according to the measurement configuration.

In another example, the base station may instruct to provide ameasurement report by sending a notification that the target cell is aborder cell to the UE in RRC inactive mode. In that case, the UEreceives in advance a measurement configuration including an event thatthe UE is located in a border cell as a triggering event for stipulatinga transmission of the measurement configuration by the UE in RRCinactive mode (e.g., the UE receives in advance when in theRRC-connected state, the measurement configuration), and upon receivingthe notification that the target cell is a border cell from the basestation, the UE transmits the measurement report to the base station.

Then, the base station determines whether to change the border cell towhich the UE is currently attached based on the measurement reportreceived from the UE. When the base station decides to change the bordercell to which the UE is currently attached into an inner cell locatedinside border cells controlled by the base station, the base stationinstructs the UE not to provide the measurement report any more. Inother words, the base station can reduce battery consumption andsignaling load of the UE by having the measurement report provided onlywhen the UE is located in the border cell.

As shown in FIG. 6, for example, the UE 610 in RRC inactive state movesto another cell to determine a cell change, and the UE 620 that hasmoved to another cell transmits a cell change request message to thebase station. The base station performs a cell changing procedurebecause the target cell belongs to the cells controlled by the basestation. The base station may recognize that the UE 620 is located inthe border cell and instruct the UE 620 to provide the measurementreport. The base station determines a cell change or a handover based onthe measurement report received from the UE 620. Then, the UE 630 movedback to the inner cell transmits a second cell change request message tothe base station. The base station is responsive to the message of theUE 630 requesting the cell change to the inner cell, for performing acell changing procedure while instructing the UE 630 to provide themeasurement report no more.

According to another embodiment of the present disclosure, the basestation can manage mobility efficiently through a separate management ofborder cells among the cells under its management. In present exemplaryembodiment, the system information broadcasted by border cells includesa flag or an indicator indicating the border cell identity. For example,embodiments may use some of the predetermined number of bits indicatingthe cell identifier included in the system information, for indicatingwhether the relevant cell is a border cell. Accordingly, the UE in RRCinactive state may recognize that the selected cell is a border cell byusing the system information received from the border cell, determinewhether to perform the measurement report by recognizing the bordercell, and determine whether to request the cell change. Further detaileddescription will be provided with reference to FIGS. 8 and 9.

FIG. 8 is a flowchart of a mobility management method of a UE, accordingto yet another embodiment of the present disclosure.

In the RRC inactive state, the UE determines whether it is needed tochange the currently attached serving cell (S810). At this time, the UEmay determine whether to change the serving cell based on at least oneof a radio signal strength of a serving cell, a radio signal strength ofone or more neighboring cells, an offset of the serving cell and each ofone or more neighboring cells, and how long a condition for the UE tomake a cell change lasts.

When it determines a cell change is needed, the UE in RRC inactive statereceives system information from the target cell (S820). Here, thesystem information includes essential information and optionalinformation as information that one cell broadcasts. For example,essential system information may include Master Information Block (MIB),System Information Block (SIB) 1, and SIB 2. The UE may obtain, from thesystem information, the cell identifier, information on the base stationthat controls the cell, and information on whether the cell is a bordercell.

The UE in RRC inactive state determines whether the base stationcontrolling the target cell is identical to the base station controllingthe serving cell based on the received system information, and performsthe cell changing procedure when the same base station equally controlsthe serving cell and the target cell. However, in this embodiment, theUE determines whether a cell change request to the base station isneeded before performing the cell changing procedure (S830).

For example, the UE may check to see whether the target cell is a bordercell of the base station controlling the serving cell, to determinewhether a cell change request is required. In this case, when the targetcell is a border cell, the UE transmits a cell change request messageincluding information on the target cell to the base station controllingthe serving cell (S840). When the target cell is not a border cell, theUE transmits no cell change request message. In addition, the UE maycheck its battery state to determine whether a cell change request isneeded. In this case, when the battery state is below a predeterminedlevel, the UE does not transmit a cell change request message includinginformation on the target cell to the base station controlling theserving cell. As long as the battery state is not lower than thepredetermined level, the UE does transmit a cell change request messageto the base station.

FIG. 9 is a flowchart of a mobility management method of a UE, accordingto yet another embodiment of the present disclosure.

The UE in RRC inactive state may receive the system information from thetarget cell or the serving cell (S910). For example, the UE maydetermine the cell change to the target cell and receive the systeminformation from the target cell or periodically receive the systeminformation from the serving cell. The UE may obtain, from the systeminformation, the cell identifier, information on the base station thatcontrols the cell, and information on whether the cell is a border cell.

The UE in RRC inactive state may determine, based on the received systeminformation, whether to transmit the measurement report to the basestation (S920). For example, the UE may check, based on the systeminformation, to see whether the target cell is a border cell of the basestation that controls the serving cell, and determine whether totransmit the measurement report. In this case, when the target cell is aborder cell, the UE transmits a measurement report according to themeasurement configuration to the base station that controls the servingcell. When the target cell is not a border cell, the UE transmits nomeasurement report according to the measurement configuration to thebase station that controls the serving cell.

In addition, the UE may determine whether to transmit a measurementreport by checking its battery state. In this case, when the batterystate goes below a preset level, the UE does not transmit themeasurement report according to the measurement configuration to thebase station that controls the serving cell, and as long as the batterystate is not less than the preset level, the UE does transmit themeasurement report according to the measurement configuration to thebase station that controls the serving cell (S930).

The above description referring to FIGS. 6 to 9 is an illustration of amethod of managing mobility by dividing cells controlled by one basestation into two types, border cells and inner cells. However,embodiments of the present disclosure are not limited to the above, andthe mobility can be managed by dividing cells controlled by one basestation into a further variety of categories. For example, cells may bedivided into cells located in the outermost region (the first group),cells located in the middle region (second group), and cells located inthe innermost region (third group). At least one embodiment may providethe following setting: When the UE in RRC inactive state selects a cellbelonging to the first group, it sends a measurement report and a cellchange request message to the base station. When the UE selects the cellbelonging to the second group, it provides no measurement report, whiletransmitting the cell change request message to the base station. Whenthe UE selects the cell belonging to the third group, it transmitsneither a measurement report nor a cell change request message to thebase station.

FIG. 10 is a schematic diagram of a configuration of a base stationapparatus 1000 according to at least one embodiment of the presentdisclosure.

The base station apparatus 1000 includes a transmission/reception unit1010 and a control unit 1020. Respective components of the base stationapparatus 1000 may be implemented as a hardware chip, or may beimplemented as software with a microprocessor being implemented toexecute the software functions corresponding to the respectivecomponents.

The transmission/reception unit 1010 transmits and receives signals toperform communication with other network function nodes and UEs.

In at least one embodiment, the control unit 1020 receives a cell changerequest message from a UE in RRC inactive state, and determines whetherthe base station 1000 is identical to the base station that controls thetarget cell, to which the UE has requested to change. The control unit1020 performs, depending on the identity or difference between the basestation 1000 and the base station controlling the target cell, ahandover procedure from the base station controlling the target cell, ora cell change procedure to the target cell.

In another embodiment, the control unit 1020 receives a measurementreport from the UE in RRC inactive state, and determines, based on thereceived measurement report, whether the UE in RRC inactive state is tochange the currently attached serving cell. When the control unit 1020determines to change the serving cell, it performs a handover procedureto the base station controlling the target cell or performs a cellchange procedure to the target set, according to whether the basestation 1000 is identical to the base station controlling the target.

When the control unit 1020 finds that it is different from the basestation controlling the target, it controls to perform the handoverprocedure to the base station controlling the target cell. When thecontrol unit 1020 finds that the base station 1000 is identical to thebase station controlling the target cell, it performs the cell changeprocedure to the target set.

FIG. 11 is a schematic diagram of a configuration of a terminal device1100 according to at least one embodiment of the present disclosure.

The terminal device 1100 includes a transmission/reception unit 1110 anda control unit 1120. The respective components of the terminal device1100 may be implemented as a hardware chip, or may be implemented assoftware with a microprocessor implemented to execute the softwarefunctions corresponding to the respective components.

The transmission/reception unit 1110 transmits and receives signals toperform communication with other network function nodes and a basestation.

The control unit 1120 in RRC inactive state determines whether to changethe currently attached serving cell. When the control unit 1120determines to change the serving cell, it receives system informationfrom the target cell and determines, based on the received systeminformation, whether the base station controlling the target cell isidentical to the base station controlling the serving cell. The controlunit 1120 performs, depending on the identity or difference between thebase station controlling the target cell and the base stationcontrolling the serving cell, releasing the RRC connection and therebytransitioning to an idle state, or a cell change procedure to the targetcell.

Although the steps in FIGS. 2 to 5 and FIGS. 7 to 9 are described to besequentially performed, they merely instantiate the technical idea ofsome embodiments of the present disclosure. In other words, variousmodifications, additions, and substitutions are possible by changing thesequences described in the respective drawings or by performing two ormore of the steps in parallel, and hence the steps in FIGS. 2 to 5 andFIGS. 7 to 9 are not limited to the illustrated chronological sequences.

The mobility management method of some embodiments illustrated in FIGS.2 to 5 and FIGS. 7 to 9 can be implemented by a program and can berecorded on a computer-readable recording medium. The computer-readablerecording medium on which the program for implementing the mobilitymanagement method of some embodiments, includes any type of recordingdevice on which data that can be read by a computer system arerecordable.

Although exemplary embodiments of the present disclosure have beendescribed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the idea and scope of the claimedinvention. Therefore, exemplary embodiments of the present disclosurehave been described for the sake of brevity and clarity. The scope ofthe technical idea of the present embodiments is not limited by theillustrations. Accordingly, one of ordinary skill would understand thescope of the claimed invention is not to be limited by the aboveexplicitly described embodiments but by the claims and equivalentsthereof.

What is claimed is:
 1. A method for managing mobility of a mobileterminal in a telecommunication network, the method comprising:performing, by the mobile terminal in a Radio Resource Control(RRC)-INACTIVE state, measurements for a serving cell and at least oneneighboring cell to enable a cell reselection process, wherein themobile terminal in the RRC-INACTIVE state maintains a connection with anAccess and Mobility Management Function (AMF) of a core network duringthe cell reselection process; choosing, by the mobile terminal in theRRC-INACTIVE state, a cell to camp from the serving cell and the atleast one neighboring cell according to the measurements and a cellreselection criteria; and by the mobile terminal, accessing a servingbase station in order to inform the serving base station of the cellchosen in the cell reselection process, wherein the serving base stationkeeps context information of the mobile terminal in the RRC INACTIVEstate and updates the context information of the mobile terminal in theRRC INACTIVE state in response to notification of the cell chosen in thecell reselection process, and wherein the method further comprises: bythe serving base station of the serving cell, performing a paging of themobile terminal in the RRC-INACTIVE state in response to the servingbase station receiving downlink data associated with the mobile terminalin the RRC-INACTIVE state from a User Plane Function (UPF) of the corenetwork; and by the serving base station, notifying the AMF of the corenetwork that delivery of the downlink data has failed when the servingbase station fails to contact the mobile terminal.
 2. The method ofclaim 1, further comprising: monitoring, by the mobile terminal in theRRC-INACTIVE state, system information from the cell chosen in the cellreselection process.
 3. The method of claim 1, wherein, when delivery ofthe downlink data to the mobile terminal has failed and the cell chosenin the cell reselection process is controlled by another base station,the downlink data is forwarded to the other base station.
 4. The methodof claim 3, wherein the serving base station sends the downlink data tothe AMF of the core network, when the serving base station fails tocontact the mobile terminal when attempting delivery of the downlinkdata.
 5. The method of claim 3, wherein the serving base station sendsthe downlink data to the UPF of the core network, when the serving basestation fails to contact the mobile terminal when attempting delivery ofthe downlink data.
 6. The method of claim 1, further comprising:attempting, by the serving base station and based on receiving thedownlink data, to activate the RRC-connected state with the mobileterminal.
 7. The method of claim 1, wherein maintaining the connectionbetween the mobile terminal in the RRC-INACTIVE state and the AMF of thecore network during the cell reselection process includes: maintaining aNon-Access Stratum (NAS) signaling connection between the mobileterminal and the AMF.
 8. A base station supporting mobility of a mobileterminal in a telecommunication network, wherein the mobile terminal ina Radio Resource Control (RRC)-INACTIVE state is allowed to choose asuitable cell to camp from a serving cell and at least one neighboringcell according to a cell reselection criteria by performing measurementsfor the serving cell and the at least one neighboring cell to enable acell reselection process, the base station comprising: means forreceiving downlink data associated with the mobile terminal in theRRC-INACTIVE state from User Plane Function (UPF) of the core network;means for keeping context information of the mobile terminal in the RRCINACTIVE state; and means for updating the context information of themobile terminal in the RRC INACTIVE state in response to notification ofthe cell chosen in the cell reselection process, wherein the mobileterminal in the RRC-INACTIVE state maintains a connection with an Accessand Mobility Management Function (AMF) of a core network during the cellreselection process, and wherein the base station further comprises:means for performing a paging of the mobile terminal in the RRC-INACTIVEstate in response to the serving base station receiving downlink dataassociated with the mobile terminal in the RRC-INACTIVE state from aUser Plane Function (UPF) of the core network; and means for notifyingthe AMF of the core network that delivery of the downlink data hasfailed when the base station fails to contact the mobile terminal. 9.The base station of claim 8, wherein, when delivery of the downlink datahas failed and another base station controls the cell chosen in the cellreselection process, the downlink data is forwarded to the other basestation.
 10. The base station of claim 8, further comprising: means forsending the downlink data to the AMF of the core network, when the basestation fails to contact the mobile terminal when attempting delivery ofthe downlink data.
 11. The base station of claim 9, further comprising:means for sending the downlink data to the UPF of the core network, whenthe first base station fails to contact the mobile terminal whenattempting delivery of the downlink data.
 12. The base station of claim8, wherein the mobile terminal in the RRC-INACTIVE state maintains aNon-Access Stratum (NAS) signaling connection between the mobileterminal and the AMF.